1. Field of the Invention
This invention relates to a structure for controlling operations of a means for supplying secondary air to an exhaust system, and a throttle opener provided on a carburetor in a suction system, for an internal combustion engine mounted on a motorcycle.
2. Description of the Prior Art
In an internal combustion engine mounted on a motorcycle, it is generally known that an exhaust gas-cleaning secondary air is supplied to an exhaust system for the engine to eliminate unburnt noxious components from an exhaust gas, and that, when the engine is rotated at a low speed, a throttle is opened slightly by a throttle opener provided on a carburetor in a suction system for the engine, to increase a suction rate of air and thereby promote the combustion of a gaseous mixture, whereby a discharge rate of unburnt components in the exhaust gas can be minimized. However, when an exhaust gas-cleaning secondary air is supplied sufficiently to the exhaust system at such time that the motorcycle runs at an extremely low speed, a comparatively large amount of unburnt components of an exhaust gas, which is discharged from the engine, and the secondary air supplied to the exhaust system react with each other actively in the exhaust system. Consequently, the exhaust system, especially, an exhaust pipe and a muffler therein are heated to a comparatively high temperature since the wind occurring as the motorcycle runs at such a low speed does not substantially serve to cool them. This often causes the color of films of chromium, which are formed on the outer surfaces of the exhaust pipe and muffler, to be changed or lost, so that the commercial values of these parts decrease. In addition, while the motorcycle runs at such a low speed that is not more than a predetermined level, the effect of engine brake decreases slightly due to an operation of the throttle opener.